Method and apparatus for continuously degassing a liquid



A. KRAFT 3,229,445

METHOD AND APPARATUS FOR CONTINUOUSLY DEGASSING A LIQUID Jan. 18, 1966 3 Sheets-Sheet 1 Filed June 21, 1961 w T0 VACUUM PUMP 3-1464) VALVE INVENTOR A. L. KRAF T 3 KMW A 7' TOFPNE V Jan. 18, 1966 A. L. KRAFT 3,229,445

METHOD AND APPARATUS FOR GONTINUOUSLY DEGASSING A LIQUID Filed June 21, 1961 3 Sheets-Sheet 2 SOLENOID STRIP /5 HEA TEA 6\. Alb- 11 A TTO/PNE V METHOD AND APPARATUS FOR GONTINUOUSLY DEGASSING A LIQUID Filed June 21, 1961 A. L. KRAFT Jan. 18, 1966 3 Sheets-Sheet 5 INVENTOR AL. KRAFT ATTOPNEV United States Patent 3,229,445 METHOD AND APPARATUS FOR CONTINUOUSLY DEGASSING A LlQUlD August L. Kraft, Roselle Parlr, N.J., assignor to Automatic Process Control, Inc., Union, N..l., a corporation of New Jersey Filed June 21, 1961, Ser. No. 118,571 11 Claims. (Cl. 5543) This invention relates to continuously operating apparatus and method for providing a flow of degassed liquid to produce coatings free from voids caused by entrapped gases. Dissolved or entrapped gases and other volatile materials are rapidly removed from the liquid by means of vacuum and heat. The utilization flow of the liquid may be either contiuous or intermittent. The equipment will handle a broad range of liquid or hot melt materials which are used in the production of various types of castings, encapsulations, coatings, etc. Such materials may include epoxies, urethanes, polyesters, vinyl plastics, petroleum and coal tars, waxes, etc.

It is a primary object of the invention to provide apparauts and control circuits to rapidly and thoroughly degas a closely controlled amount of heated liquid, thus overcoming the well known disadvantages of degassing the relatively large amounts involved in the use of batch methods. This is accomplished by bringing the temperature of the material up to some optimum point (usually pour temperature) so as to reduce its viscosity and by removing all air from the material before it moves on to a utilization stage.

A major feature of the invention resides the provision of means to create a thin film of liquid of substantially uniform thickness, to produce motion of said film while subjecting it to heat and vacuum to remove gases therefrom, to propel said degassed liquid to a utilization station on demand, and to maintain said film in motion regardless of whether or not there is demand by the utilization station.

A feature of the invention is the use of both rough and film degassing stages. For this purpose the heated material is caused to flow over the top edge of a cylinder to produce a uniformly thin film which may be subjected 'to vacuum to remove gases.

A further feature of the invention resides in the provision of a heating element of large surface area continuously immersed in the moving liquid.

An added feature may be found in the use of a sensing device having variable thermo-resistive properties in the form of a conductor also continuously immersed in the liquid.

In accordance with still another feature, the material may be continuously recirculated while being kept heated and at a fixed reserve level on occasions when there is no output demand from the utilization equipment.

Additional features include adjustable rates of flow, both into and out of the device, immersible probes to sense liquid levels at a plurality of locations, and electrical circuits to control the progressive and cyclic operation of the machine.

These and other objects and features of the invention will be more completely understood from the following detailed description, reference being had to the accompanying drawings.

In the drawings:

FIG. 1 is a side elevation, partly in section, of the assembled device.

FIG. 2 is a sectional view taken on the line 2-2 of FIG. 1.

FIG. 3 is a circuit diagram showing control circuits in their relation to various electrical components of the machine.

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'FIG. 4 is a circuit diagram showing the heat-sensing circuit in detail.

Referring now to the drawing, a base member 1 is supported by the legs of a tripod which is adjustably secured to a plate 2. Two of the legs of the tripod are shown at 33, and are adjust-ably mounted by means of threaded sections so that a level mounting of the device may be achieved readily. A heavy glass cylinder 4 is hermetically sealed to base member 1 in any convenient manner, a suitable method of completing this seal being the use of clamped 0 rings. The large outer glass cylinder supports a cap member -5 which is also hermetically sealed to the glass cylinder. An air motor 6 is mounted on cap 5 by way of tubular throat 7 and is sealed against air leaks to the interior of cylinder 4. Air motor 6 is provided with a long shaft 8 which extends downward to an aperture in the base member in which a pump impeller 9 is rotatably mounted to urge the contents of the degasser into a utilization tube 10. An aluminum inner cylinder 11 is mounted on a cylindrical extension of base member 1 and is secured to said member and sealed therefrom in any convenient manner.

As best seen in FIG. 2, a series of notched vanes 12 are circumferentially mounted on aluminum cylinder 11. These vanes are preferably composed of a suitable plastic and may be secured to the aluminum cylinder by means of pins 13 which lie in short slots in cylinder 11 to permit differential thermal expansion between the cylinder and the vane 12. As may be seen by inspection of the sectionalized portion of cylinder 11, the notches in vanes 12 are alternately wide and narrow in extent. The notches appear at progressively higher positions in the vanes so that conductors inserted therein will assume the form of a helix. A flat strip 15 is helically wound about the vanes 12 and is supported by the wider notches in vanes 12. This helical strip provides a heating element of very large surface area. Electrical connections to the strip are indicated at 16 and 17. A sensing wire 18 is helically wound and supported by the narrow notches in vanes 12. The sensing wire forms one element of a temperature control circuit, the operation of which will be more fully described hereinafter. Connections to conductor 18 may be made by means of lead-in conductors 19 and 20. A heater conventionally indicated at 21 is provided 'to heat base 1.

An inlet valve indicated generally at 22 permits flow of material to be degassed from a reservoir 24 via tube 25 to passages 26 and 27 which have been bored in base member 1. Passage 27 permits discharge into the annular space between outer glass cylinder 4 and inner aluminum cylinder 11. A diaphragm 23 may be forced into closed position under manual control by threaded member 28, but when the machine is in automatic operation member 28 is 'backed out to free the diaphragm for control via tube 29 which extends to the three-way valve which will either apply air pressure to the diaphragm via tube 30 or vacuum suction by way of tube 31. Three-way valve 32 maybe operated into its alternate positions under the control of solenoid 33 which, when energized, applies suction to the back of diaphragm 23 to open valve 22 to permit flow of material into the degasser. With solenoid 33 deenergized, valve 32 is moved to its alternate position, in which position atmospheric pressure via tube 30 permits diaphragm 23 to close valve 22.

Tube 31 extends to a vacuum pump not shown. The

degree of vacuum may be adjusted to a desired value depending primarily on the viscosity of the material to be degassed. Vacuum may be applied to the interior of the device by way of a tube 34 which branches from tube 31 extending to the vacuum pump. Connection from the 3 interior of the degasser is via throat 7 previously described.

A bored passage 35 extends to another diaphragm control valve indicated generally at 36. A resilient diaphragm 37 is forced to the left, as seen in the drawing, when pressure is built up in tube 35, which will occur when there is no demand at the utilization station. In this situation recirculation of the material takes place via bored out passages 38 and 39. It will be noted that passage 39 opens into the annular space between glass cylinder 4 and inner cylinder 11. A source of air under pressure is connected to tube 40 and extends to a valve 41 which is branched to apply air pressure to both air motor 6 and the back of diaphragm 37 via a relief valve 42 and tube 43. Valve 41 may be adjusted to regulate the speed of air motor 6, and relief valve 42 may be adjusted to create pressure to a desired extent on the back of diaphragm 37.

Cap member also supports liquid level sensing probes 44 and 45 and conductors 46 and 47 extending thereto. It should be noted that probe 45 is physically situated directly over the intake supply line via bore 27. The functions of probes 44 and 45 will be made evident in the course of describing the operation of the machine.

The operation of the device will now be described, reference being bad to the circuit diagram of FIG. 3 wherein components illustrated in FIG. 1 have been designated by like numerals wherever possible. It will be assumed that preliminary adjustments have been made and that the device is ready for operation. It will also be assumed that the machine is empty, having been purged after completion of previous use.

Closure of master switch 50 connects a source of 115 volt alternating current to bus conductors 51 and 52. A red lamp 53 provides information as to the closure of the master switch. At the same time base heater 21 is energized via switch 50 and conductors 51, 54 and 52.

Spring returned FILL switch 55 is then moved to engage its alternate contacts. The upper contact of this switch closes an obvious circuit for solenoid 33 extending from common conductor 52 through master switch 50 to the power supply. Solenoid 33 is energized to operate valve 32 (FIG, 1) to apply vacuum to the diaphragm of valve 22. With the vacuum pump in operation, suction will be applied to the interior of the glass cylinder, and the liquid material will flow from reservoir 24 through tube 25, valve 22 and bores 26 and 27 into the annular space between the aluminum cylinder 11 and external glass cylinder 4. As the material rises, it will be kept under visual observation through the glass until it commences to flow over the top rim of cylinder 11 and down the inner wall therof. Inasmuch as the top rim of the cylinder 11 has been caused to lie in a horizontal plane by adjustment of tripod legs 33, the film will be of uniform thickness.

At this time the helical heater strip 15 may be energized by momentary closure of manual switch 56.

It should be noted that closure of master switch 50 en ergized primary windings 57, 58 and 59 in parallel with each other and with base heater 21. Windings 57, 58 and 59 apply power to primary level control 60, liquid level control 61 and temperature control 62. Control circuits 60 and 61 supply operating energy for relays 63 and 64 respectively. They are conventional, commercially available circuits and will not be described in detail. They respond to capacity variations in probes 45 and 44 (FIG. 1) and their operation is such that energizing potential is supplied to the relays at such times as the probes are immersed in liquid.

Temperature control 62 supplies energy to its associated relay 65 whenever the temperature of the liquid falls below a selected value. The temperature control circuit responds to variations in the resistance of sensing wire 18. The operation of the temperature control circuit will be described hereinafter.

It may be noted that during the preliminary filling operation the temperature control circuit will be in a condition to indicate that heat should be supplied to the liquid. At this time relay 65 cannot operate because its normal circuit is open at the outer contact of relay 66. The manual closure of switch 56 will energize relay 65 and close an obvious circuit for heater 15. A yellow lamp 67 is connected in parallel with heater 15 to indicate to the operator that the heater is energized. Switch 56 should be closed for short intervals only until the helical heater strip is completely immersed. After this occurs, continued closure of switch 56 is safe because over-heating of the material will be prevented when the control circuit 62 recognizes that the desired temperature has been reached.

As soon as the liquid begins to flow over the lip of cylinder 11, probe 45 signals primary control circuit 60, which supplies energizing potential to relay 63 by way of the lower arm and contact of FILL switch 55. Relay 63, upon energization, completes a locking circuit for itself by way of its right hand armature. Relay 63 is continuously energized so long as probe 45 is immersed in liquid.

With material flowing down into cylinder 11, a start key 68 is momentarily depressed and switch 55 is released. The momentary closure of switch 68 completes an obvious circuit for primary control relay 69 by way of conductor 54 and switches 68 and 50. Upon energization, relay 69 completes a locking circuit for itself by way of stop switch 70. The locking circuit of relay 69 also provides a continuing circuit for red signal lamp 72 which was originally lighted upon depression of start key 68. With relay 69 energized, a circuit is completed from conductor 54 downward through the winding of a secondary control relay 66, front contact and left armature of relay 63 and conductor 74 to the closed contact of relay 69. Relay 66 energizes and at its outer armature establishes a circuit whereby relay 65 is placed under control .of temperature control 62. It will be recalled that switch 56 was opened as soon as the liquid began to flow into the interior of cylinder 11.

The energization of relay 66 completes a circuit for amber lamp 73 which lights to indicate to the operator that the device is under automatic operating condition.

With switch 55 in its normal position, the extent to which the cylinder 11 will be filled is under the control of circuit 61. Until probe 44 is covered by the liquid, relay 64 is deenergized, maintaining the circuit of solenoid 33 by way of the upper normal contacts of switch 55, armature and back contact of relay 64 and armatures and contacts of relays 66 and 69.

With material flowing over the top of the aluminum pipe, the air motor may be started under control of valve 41. The output line should now be opened and the motor speed regulated so that the pump is driven slowly, but fast enough to move material out of the degasser against internal vacuum. Control valve 22 is now adjusted by means of thumb screw 28 to a position such that material enters the degasser at a rate faster than the pump is pushing it out. Thus a reservoir of material is built up inside of cylinder 11 from its base, and when this builds up to the desired height, probe 44 is immersed in the material and signals control circuit 61, whereupon relay 64 is energized to open the circuit of solenoid 33, which, upon deenergization, closes the input valve. The energization of relay 64 completes a circuit for amber lamp 75 to notify the attendant that the material within the cylinder has attained a desired level.

As demand is made by the utilization station, the column of reserve material will fall until probe 44 is no longer immersed, whereupon relay 64 is deenergized to close the circuit of solenoid 33 which permits flow into the degasser. During this operation the extinguishing of lamp 75 notifies the attendant that such flow is taking place. Repeated operation of relay 65 as the control circuit responds to the temperature condition of sensing wire 18 maintains the material at a temperature which is regulated within close limits.

As has been previously described, in case there is no demand at the utilization station, recirculation of the material takes place under control of relief valve 36. Thus a moving film of uniform thickness and of selected temperature is at all times exposed to and has its gas content removed by the vacuum within the degasser.

If the supply of liquid in storage tank 24 is exhausted, air will flow into the degasser and create air bubbles at the point where bore 27 vents into the liquid column. These bubbles will rise rapidly and when they strike probe 45, which it will be recalled is located directly over bore 27, the presence of these bubbles will be immediately sensed by probe 45. The changed dielectric condition of probe will influence primary liquid control circuit 66, which will reduce its output power potential and cause its associated relay 63 to deenergize. Upon deenergization, the left-hand armature and back contact of relay 63 closes an alarm circuit extending from conductor 76 through an alarm device 77 to conductor 74 and thence to the other side of power supply. Alarm device '77 produces an audible signal to notify the attendant that the supply of liquid in the reservoir has been exhausted.

The left-hand armature of relay 63 also deenergizes relay 66 which extinguishes both amber lamps and at its outer armature opens the circuit of temperature control relay so that no heat can be automatically applied to the liquid until a new tank supply has been established.

Momentary operation of stop switch at any time will open the locking circuit of control relay 69 and restore the circuit to its normal condition.

After a new supply of liquid has been furnished to reservoir 24, or a full tank equivalent to tank 24 substituted therefor, refilling of the machine and its subsequent operation will take place as previously described.

Referring now to FIG. 4, the temperature control circuit Will be described. This unit is basically a bridge circuit, the sensing wire 18 constituting one arm of the bridge. The output of the bridge when unbalanced is fed to an amplifying circuit to provide rectified current to control the operation of relay 65.

Inasmuch as the sensing wire is immersed throughout its length in the liquid and is in close proximity throughout its length to the heating element, it is obviously in a position to provide temperature control within very narrow limits. A problem arises, however, due to the close inductive coupling between the turns of the sensing wire and the turns of the heater strip. Alternating currents induced in the heater strip will tend to produce considerably greater unbalance of the bridge than the changes produced by variations in the electrical resistance of sensing wire 18, due to changing temperatures. It is the function of the circuit of FIG. 4 to neutralize the effect of such currents.

Transformer primary 59, previously mentioned in connection with the circuit of FIG. 3, supplies energy to winding 78 which forms the secondary transformer winding. A center tap on winding 78 is connected to ground. The divided secondary provides two arms of an alternating current bridge. A third arm includes a variable resistor 79 and a fixed resistor 89. With the bridge in balance no potential would normally exist between the junction of sensing wire 18 and resistor 80 and the grounded midpoint of winding 78. Relay 65, which as has been previously described supplies switching for the heater strip, is connected across the output of winding 78 in series with an amplifier controlled rectifying transistor 84.

From the junction of resistor 80 and sensing wire 18 error signals are fed through a resistor 89 to the base of a PNP transistor 81. Also applied to the base of this transistor is a constant current derived from a six-volt Zener diode 82. This constant current may be adjusted by means of a potentiometer 83 so that when the bridge is balanced, i.e., when the voltage at the junction of sensing wire 18 and resistor 8!) is zero with respect to ground, there is just enough current through the collector of transistor 81 to permit current fiow through transistor 84. Thus any deviation from zero of the null on the bridge circuit is enough to cause transistor 81 to either draw more or to draw less current, and so causes transistor 84 to be either conducting or nonconducting. Zener diode 82 supplies a constant voltage swing of six volts and thus supplies a constant current to the base of transistor 81. Since the collector of transistor 81 is a constant current source if the base current input is constant, the result of this circuit configuration is to stabilize the circuit for large line voltage variations. A diode 85 is used to supply transistor 81 with half-wave rectified direct currentwhich is negative with respect to ground. This circuit includes a resistor 91. This half-wave rectified voltage is in phase with the positive-going alternating current on the electrodes of transistor 84 to which it is supplied via resistors 88 and 92. A diode 86 prevents any negative-going pulses from being applied to transistor 84 during the time it is in conducting condition.

A diode 87 prevents large positive excursions between the base and emitter of transistor 81.

What is claimed is:

1. A liquid degassing system including a liquid inlet means, means associated with said liquid inlet means for forming a uniform moving liquid film, means to apply heat to said liquid film and means to subject the said liquid film to vacuum whereby said liquid is degassed, a reservoir positioned to receive said degassed liquid film, means to maintain a desired liquid level in said reservoir by automatic control of said liquid inlet means, means to continuously withdraw liquid from said reservoir, means for delivery of any portion of said withdrawn liquid on demand to a utilization station and means to recycle to said liquid inlet means liquid which is withdrawn from said reservoir but not delivered to said utilization station.

2. A vertical cylindrical column, a hollow cylinder nested within said column with its top edge substantially horizontal, liquid inlet means for introducing liquid to the annular space between the column and the cylinder enclosed thereby, means to apply heat to said cylinder and means to subject the interior of said cylinder to vacuum, a closure for the bottom of said cylinder whereby a reservoir for said liquid is formed in the lower portion thereof, means to control the level of liquid in said reservoir by automatic control of said liquid inlet means, a pump to continuously withdraw liquid from said reservoir, means for delivery of any portion of said withdrawn liquid to a utilization station on demand, means to recycle to said annular space liquid which is withdrawn from said reservoir but not delivered to said utilization station.

3. A vertical cylindrical column, a hollow cylinder nested within said column and having a substantially horizontal top edge, liquid inlet means for intnoducing liquid to the annular space between the column and the cylinder enclosed thereby, a thermostatically controlled heater disposed about said cylinder, means to apply vacuum to the interior of said cylinder, a closure for the bottom of said cylinder whereby a reservoir for said liquid is formed in the lower portion thereof, means to control the level of liquid in said reservoir by automatic control of said liquid inlet means, a pump to continuously withdraw liquid from said reservoir, means for delivery of any portion of said withdrawn liquid on demand to a utilization station and means to recycle liquid withdrawn from said reservoir but not delivered to said utilization station.

4. A base member, a vertical cylindrical column supported thereby, a hollow cylinder nested within said column and also supported by said base member with the upper edge of said cylinder horizontal, liquid inlet means for introducing liquid to the annular space between the column and the cylinder enclosed thereby, means to apply vacuum to the interior of said cylinder, :1 thermo statically controlled heater disposed about said cylinder, a closure for the bottom of said cylinder whereby a reservoir for said liquid is formed in the lower portion thereof, means to control the level of liquid in said reservoir by automatic control of said liquid inlet means, a pump to constantly withdraw liquid from said reservoir, means for delivering the output from said pump on demand to a utilization station, means for recycling through said annular space liquid withdrawn from said reservoir but not delivered to said utilization station, an auxiliary-heater associated with said base and means to apply electrical energy to said auxiliary-heater.

5. Apparatus according to claim 4 wherein said means for recycling liquid which is withdrawn from said reservoir but not delivered to said utilization station includes a relief valve and liquid conduit means.

6. Apparatus according to claim 4 wherein said thermostatically controlled electrical heater includes vanes mounted longitudinally on the exterior wall of said cylinder, a heating element of large surface area in the form of a helical strip supported by said vanes and temperature sensitive means for controlling operation of said heating element.

7. Apparatus according to claim 6 wherein said temperature sensitive means includes a helical sensing wire supported by said vanes progressively interposed between the convolutions of the heating element and means responsive to variations in the resistivity of said sensing wire with changes in temperature for controlling operation of said heating element.

8. Apparatus according to claim 7 wherein said means for controlling said heating element is responsive to variations in resistivity of said sensing wire with changes in temperature but non-responsive to effects produced in said wire by the inductive coupling between said heating element and said sensing wire.

9. Apparatus according to claim 4 which further in cludes a protective circuit operative to generate a signal when the supply of liquid to said annular space is exhausted.

10. A liquid degassing apparatus which includes:

(A) A first hollow column having first and second ends;

(B) A second hollow column having first and second ends and fixedly located within said first column, said first and said second columns defining a space therebetween; said first end of said first column and said first end of said second column being adjacent;

(C) Base means enclosing each said first end of said first and second columns;

(D) Means enclosing said second end of said first column, said second end of said second column being open with its edge lying in a plane transverse to its axis, said plane intersecting said first column intermediate its first and second ends;

(E) Heating means disposed about said second column in the space defined between said first and second columns;

(F) Means for subjecting the interior of said second column to vacuum;

(G) Inlet conduit means for introducing liquid to the lower portion of the space defined between said first and second columns;

(H) Liquid pumping means having an inlet and an outlet;

(I) Outlet conduit means interconnecting said first end of said second column with the inlet of said liquid pumping means whereby liquid can be continuously withdrawn from said first end of said second column;

(I) Utilization conduit means connected to the outlet of said liquid pumping means whereby any portion of said withdrawn liquid can be delivered to a utilization station on demand;

(K) Recirculation conduit means interconnecting the outlet of said liquid pumping means with the space defined between said first and second columns whereby liquid withdrawn from said first end of said second column but not delivered to said utilization station is recycled to said space;

(L) Means for controlling the level of liquid in said second column by controlling the flow of liquid through said inlet conduit means.

11. The method of continuously degassing a liquid which includes providing a controlled inlet flow of said liquid heating said liquid, forming a uniform moving film of said liquid, subjecting said moving film to vacuum to degas said liquid, collecting degassed liquid from said moving film in a reservoir, continuously withdrawing degassed liquid from said reservoir, delivering any portion of said degassed liquid to a utilization station on demand, recycling degassed liquid which is withdrawn from said reservoir but not delivered to said utilization station and combining said recycled liquid with said inlet liquid flow prior to forming said uniform moving film of said liquid and adding further inlet liquid as required to maintain a constant volume of degassed liquid in said reservoir.

References Cited by the Examiner UNITED STATES PATENTS 664,763 12/1900 Kluecker 55-42 1,734,515 11/ 1929 Elliott 55-42 1,747,193 2/1930 Taddiken 165-113 1,967,799 7/ 1934 Wittemann 210-497 2,036,417 4/1936 Laird 165184 2,111,957 3/1938 Banks et al. 55-41 2,140,607 12/ 1938 Thompson -93 2,703,699 3/1955 Carroll -132 2,721,888 10/1955 Harris 5589 2,735,840 2/ 1956 Lynch 264-102 2,755,506 7/1956 Weber 165-61 2,774,441 12/1956 Buurman 55-42 2,943,841 7/ 1960 Hughes et al 165-132 2,946,488 7/ 1960 Kraft 222-134 2,966,584 12/1960 Cervinka 55-193 3,007,919 11/1961 Hoskins 55-41 3,043,480 7/ 1962 Wittrock 222-146 3,044,236 7/1962 Bearden et al 55-270 FOREIGN PATENTS 544,058 2/ 1932 Germany. 956,584 1/ 1957 Germany.

REUBEN FRIEDMAN, Primary Examiner.

HERBERT L. MARTIN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Non 3,229,445 January 18, 1966 August Ln Kraft It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 54, for "33" read 3 column 8, line 52, for "2,966,584" read 2,966,230

Signed and sealed this 31st day of May 1966.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

1. A LIQUID DEGASSING SYSTEM INCLUDING A LIQUID INLET MEANS, MEANS ASSOCIATGED WITH SAID LIQUID INLET MEANS FOR FORMING A UNIFORM MOVING LIQUID FILM, MEANS TO SUPPLY HEAT TO SAID LIQUID FILM AND MEANS TO SUBJECT THE SAID LIQUID FILM TO VACUUM WHEREBY SAID LIQUID IS DEGASSED, A RESERVOIR POSITIONED TO RECEIVE SAID DEGASSED LIQUID FILM, MEANS TO MAINTAIN A DESIRED LIQUID LEVEL IN SAID RESERVOIR BY AUTOMATIC CONTROL OF SAID LIQUID INLET MEANS, MEANS TO CONTINUOUSLY WITHDRAW LIQUID FROM SAID RESERVOIR, MEANS FOR DELIVERY OF ANY PORTION OF SAID WITHDRAWN LIQUID ON DEMAND TO A UTILIZATION STATION AND MEANS TO RECYCLE TO SAID LIQUID INLET MEANS LIQUID WHICH IS WITHDRAWN FROM SAID RESERVOIR BUT NOT DELIVERED TO SAID UTILIZATION STATION. 